1. Technical Field
The present invention relates to sheet finishing apparatuses that stack/store sheets sequentially conveyed out from a printer, a copier, a printing machine or other device; more particularly the invention relates to sheet finishing apparatuses for receiving sheets on which images have been formed by an image forming apparatus, and carrying out stapling, punching or stamping processes on the sheets.
2. Description of the Related Art
Generally, these kinds of sheet finishing apparatuses temporarily set onto a tray sheets on which images have been formed by an image forming apparatus, etc. After the sheets set on the tray have been finish-processed, the finished sheets are held in a downstream storage tray. In the finishing tray, depending on the process, the sheets are finished by being placed on the tray one at a time to undergo a stamping process, or a ream of sheets is placed on the tray in a bundle to undergo a stapling process. This means that the finishing tray requires a conveyance mechanism for bringing in sheets, and a conveyance mechanism for sending out finished sheets to the storage tray.
Conventionally, as a conveying-in mechanism for conveying in sheets to a finishing tray, a system wherein conveyance rollers are provided at a sheet-discharge outlet of a discharge path for ejecting sheets onto a tray arranged forming a break in the path on the downstream side of the discharge outlet, and a system wherein sheets are conveyed out by the cooperation of a first discharge roller provided at a discharge outlet, and a second discharge roller arranged on a tray are both known. While the former system affords a simple structure, the downside is that sheets can become skewed or otherwise misaligned. A known problem with the latter is that sheets can become wrinkled or otherwise damaged if the timing at which the second discharge roller on the tray engages the sheets being fed by the first discharge roller is off.
Meanwhile, as a conveyance mechanism for discharging sheets from a finishing tray, a mechanism such as that disclosed in Japanese Unexamined Pat. App. Pub. No. 2003-128332, for example, is known, in which a claw-shaped projecting member is provided for engaging the trailing edge of the sheets on the finishing tray, and the projecting member is shifted along the finishing tray to convey sheets out toward a stacking tray. Specifically, a long groove is provided in the midportion of the finishing tray, reaching from the sheet-inflow side to the sheet convey-out side. The claw-shaped projecting member is disposed in the long groove to project above the tray through the tray back side (the reverse side), and is fastened to an endless belt provided along the tray back side. Pulleys for the endless belt are drivingly rotated. Pressing on the trailing edge of the sheets with a claw-shaped member in this way enables the accurate conveyance to the storage tray of weighty sheets stacked in a bundle. It also makes it possible to neatly convey the sheets out in bundle form.
A further example of such conveyance mechanisms is a system, proposed for example in Japanese Unexamined Pat. App. Pub. No. 2002-193515 among other publications, in which, along with a sheet pushing mechanism for pushing out the trailing edge of the sheets, conveyance rollers are disposed at the discharge-outlet end of the conveyance path. According to this configuration, a claw-shaped projecting member is arranged on the finishing tray, free to travel along the convey-out direction, and a conveyance roller is arranged on the downstream side of the tray to convey out sheets. Sheets set on the finishing tray are pushed out by the claw-shaped projecting member and are then conveyed out by the conveyance roller. In other words, the claw-shaped projecting member pushes the sheets along the tray and downstream, and thereafter the conveyance roller, arranged at the discharge outlet on the downstream side, separated from the claw-shaped projecting member, takes over to convey the sheets.
With such structures known to date, in which sheets are ejected onto a tray with a discharge roller at the discharge outlet, sheets can become skewed and stacked out of alignment on the tray, or stray outside the tray in implementations in which, as described above, sheets are stacked in a finishing tray, with a break in the path from the discharge outlet being formed as described above. This means that, particularly when carrying out stapling or other finishing processes, with the sheets becoming unaligned, there will be problems inviting mishandling of the sheets. Likewise, a problem with implementations in which roller means at the discharge outlet and roller means on the tray cooperate to discharge sheets, as is disclosed in the above-cited App. Pub. No. 2002-193515, is that in rotating while pressing the sheet, the roller means arranged on the tray transfers in the sheet-discharging direction the lead sheet already stacked in a predetermined position, giving rise to displacement.
Sheets already stacked on the tray slipping out of place due to subsequent sheets being conveyed into the tray can invite erroneous finishing operations in the same manner as with the situations described above. With (flimsy) sheets lacking stiffness, such displacement is the cause of corners getting bent or folded. Particularly, in implementations in which a forward/reverse rotating roller means is provided on the stacking tray, and sheets are switched back from the discharge outlet and brought into alignment by their trailing edges landing against a registration member, at the same time that the above-described problems are brought about when sheets are conveyed in, a problem arises in which, in switching-back sheets with the roller means to bring the sheets into alignment, sheets that have been stacked may get dragged along and bend or fold at the leading edges.